 # Boyles Law Formula

## Boyle’s Law Formula

Boyle’s Law, an ideal gas law which states that the volume of an ideal gas is inversely proportional to its absolute pressure at a constant temperature. The law applies only to ideal gases which allow only pressure and volume to change.

In other words, the product of pressure and volume is constant for a fixed mass of ideal gas at fixed temperature.

P1 X V1 = P2 X V2

The other way to express Boyle’s Law is as follows Where

•    P denotes pressure of the gas
•    V denotes volume of the gas
•    K is constant and holds units of force times and distance.

Example 1

Neon (Ne) sample occupies 4L at a pressure of 5 x 104 Pa and 273K temperature. Calculate the volume of the sample at STP?

Solution

Initial conditions are

P1 = 5 x 10-4Pa and V1 = 4L

Final conditions are

P2 = 101325 Pa and V2 = ?

We have an equation

P1 x V1 = P2 x V2

V2 = P1V1/P2

V2 = (5 x 104 Pa) (4L) / 1.01325 x 105 Pa

= 2 x 10 5 / 1.01325 x 105 L

Hence, V2 = 1.97 L

Example 2

A gaseous nitrogen sample in a 65L air bag has a pressure of 745 mm Hg. If this sample is transferred into a 25 L bag at same temperature, what is the pressure of the gas in 25L bag?

Solution

Initial conditions

P1 = 745 mm of Hg and V1 = 65L

Final conditions

V2 = 25L and P2 =?

We have an equation

P1V1 = P2V2

Put the above values in this equation

P2 = P1V1/V2

P2 = 745 mm of Hg x 65L / 25L

Therefore P2 = 1940 mm Hg

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